Instrument for measuring distance

ABSTRACT

A distance measuring instrument of the type wherein a modulated beam of light is transmitted along a path to be measured, the light is reflected at the distance to be measured and received at the instrument, and a comparison is made between the modulation phase of the received signal and that of the transmitted signal to determine the distance in terms of the wavelength of the modulation signal, includes an arrangement for varying the wavelength in inverse proportion to the sine or cosine of the angle of elevation whereby the measurement obtained is related to the vertical or horizontal projection of the distance irrespective of the elevation of the instrument.

Unite Stat Ptet 3,677,646 Granqvist [4 July 18, 1972 [54] INSTRUMENT FORNEASG 2,497,913 2/1950 Rines ..343/12 DISTANCE 2,964,990 12/1960 Pocher..356/5 3,256,766 6/1966 Allesson ..356/5 [72] Inventor: Carl ErikGranqvist, L1d1ngo, Sweden [73] Assignee: Aga Akflebolag, Lidingo,Sweden 'f Hammer-Benjamin Bcfrchelt ASSISIG!!! Exammer-S. C. Buczmski[22] Filed: Sept. 8,1969 An0mey--Lars0n, Taylor and Hinds 21 Appl.No.:856,130

[ ABSTRACT A distance measuring instrument of the type wherein a modu-[30] Foreign Application Priority Dam lated beam of light is transmittedalong a path to be measured, Sept. 12, 1968 Sweden 12253/68 the light isreflected at the distance to be measured and received at the instrument,and a comparison is made between 52 US. Cl ..356/4, 356/5, 343/12 themodulation Phase of the received signal and that of 5 C| 601C 3/08transmitted signal to determine the distance in terms of the 58 Field ofSearch ..343/12, 10- 356/5 4 Wavelength mdulatih Signal, includes anarrangement for varying the wavelength in inverse proportion to the sineor 56 R f Cited cosine of the angle of elevation whereby the measurementob- 1 e erences tained is related to the vertical or horizontalprojection of the UNITED T T PATENTS distance irrespective of theelevation of the instrument.

3,565,528 2/1971 White ..356/5 5 Claims, 3 Drawing Figures MODULATED 20LIGHT souRcE MODULATION SIGNAL SOURCE SHIFTER ELEVATION- RESPONSIVE 4ODEVICE Patented July 18, 1972 3 Sheets-Sheet 1 MODULATED LIGHT SOURCEMODULATION SIGNAL SOURCE PHASE COMPARATOR ADJUSTABLE PHASE SHIFTER FIG.1

mvmroas CARL- ERIK GRANQVIST BY I 504 ATTORNEYS Patented July 18, 19723,677,646

3 Shams-Shoat 2 MODULATION LIGHT SOURCE ELEVATION RESPONSIVE 28 DEVICE3O ANIQLOG-TODIGI TA L ez \PCONVERTER DEV'CE JACTUATORV MASTEROSCILLATOR A 1 j 1 54 1 4 COUNTER n 46 i l I I l f i v F o \5O f f/ l 2W 52 i 66 MIXER \FREouENcY swlTcHm 1 Mii DETECTOR CIRCUIT FREQUENCY 74CONTROLLED 64 FREQUENCY OSC'LLATOR 7O MEASURING l DEV|CE- MIXER mvsmonCARL- ERIK GRANQVIST ATTORNEYS Patented July 18, 1972 3 Sheets-Sheet 5:23 JOKPZOO/ mm. H

INVENTORS CARL-ERIK GRANQVIST Q BY (Qfi/ZSW ATTORN EYS INSTRUMENT FORMEASURING DISTANCE FIELD OF THE INVENTION BACKGROUND OF THE INVENTION Anumber of problems are presented where an instrument of the typedescribed above is elevatable so that the path along which the measureddistance is taken is different from the horizontal. It will beappreciated that measurements obtained along paths different from thehorizontal are not directly commensurate with measurements such asprovided on maps used by surveyors, these latter measurements beingplotted as horizontal distances between different points even where thedifferent points in question actually are located at differentaltitudes. Hence, in field work, where points are to be marked out withthe aid of a map of the type described, tedious corrective computationsand adjustments may be necessary because of the inclination to thehorizontal of the various measured distances. For example, one approachis to calculate the horizontal distance from the value of the inclineddistance obtained. When this approach is used it is oftentimes foundthat the point to be marked out is not located precisely where thedistant reflector was placed during the measurement procedure and acorrection becomes necessary. It is noted that on some occasions morethan one correction may be necessary in order to ensure that the correctdistance is laid out.

SUMMARY OF THE INVENTION In accordance with the present invention theprocedure set forth hereinabove is substantially simplified through theprovision of a measuring instrument which is adapted to automaticallycompute the horizontal (or vertical) distance directly. The horizontaldistance in question is the product of the inclined distance traveled bythe light signal and the cosine of the value of the angle of elevation(positive or negative) of the instrument. Of course, if desired, thevertical distance may be similarly obtained by multiplying the inclineddistance by the sine of the angle of elevation.

In accordance with the present invention an instrument is provided forautomatically varying the wavelength of the modulation signal independence upon the elevational angle, for example, in inverseproportion to the cosine of the elevation angle. In accordance with apresently preferred embodiment of the invention, the instrument includesan optical unit for transmitting a beam of light and for receiving abeam of light along the optical axis thereof, means for varying theelevation of the optical unit, a light transmitter for supplying a beamof light to be transmitted by the optical unit, a light receiver forreceiving the light received by the optical unit, a modulation signalsource connected to the transmitter for producing a modulation signalfor modulating the transmitted beam of light and having a control inputfor varying the wavelength of the modulation signal, a device formeasuring the modulation phase difference between the transmitted andreceived light, and an elevation-responsive device for generating acontrol signal in accordance with the elevation of the optical unit, thecontrol signal being applied to the control input of the modulationsignal source.

Other features and advantages of the present invention will be set forthin or apparent from the detailed description of presently preferredembodiments of the invention found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof a presently preferred embodiment of an instrument using themeasurement of horizontal distances;

FIG. 2 is a schematic representation similar to FIG. 1 showing detailsof certain of the circuitry shown schematically in FIG. 1; and

FIG. 3 is a schematic representation of one embodiment of theelevation-responsive device of the instrument in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a distancemeasurement of the coaxial type is shown, the instrument measuringdistance in a conventional manner utilizing a modulated beam of light asset forth hereinabove. Because the instrument is otherwise conventionalonly those details are shown which are necessary for an understanding ofthe invention.

Thus, referring to FIG. 1, the instrument comprises an elevatableoptical unit 10 including a tubular housing or tube 12 in which theoptical system is contained. The optical system includes a parabolicmirror 14 mounted at the rear of tube 12 and a further mirror 16 locatedcentrally in the tube 12 and arranged to receive a beam of light denoted18 from a modulatable light source 20. The beam of light 18 istransmitted in the direction of the optical axis 22 of parabolic mirror14 towards a reflector (not shown) located at the distance to bemeasured. The return beam of light, which is denoted 24, is reflected bymirror 14 towards the rear surface of mirror 16 and from thence to alight sensitive device 26 which may, for example, be a photocell. Theoutput of light sensitive device 26 is a voltage proportional to thestrength of the returned beam 24. The modulation signal is obtained froma modulating signal source 28 having a control input 30 for varying thefrequency f of the signal in dependence upon the elevation of theinstrument, according to the formula f Fcosa. The output of modulatingsignal source 28 is applied to a modulated light source 20 to modulatetransmitted beam 18. The output of source 28 is also applied to anadjustable phase shifter 32, phase shifter 32 enabling the phase of theoutput to be adjusted. The output of adjustable phase shifter 32 isconnected to a phase comparator 34 which is also connected to the outputof light sensitive device 26. The measurement of the distance inquestion is performed in a conventional manner by adjusting phaseshifter 32 until phase comparator 34 reads zero. As stated, this kind ofmeasurement is well known in the art and further explanation thereof isdeemed unnecessary.

To provide for elevation thereof, tube 12 is journalled on an axis 36supported in a support arrangement 38 indicated schematically in FIG. 1.An elevation-responsive device 40 is integrally mounted on tube 12 andresponds to the elevation of the tube 12 to produce an output current[(a) which is supplied to control input 30 of modulating signal source28 to adjust the frequency f so that f Fcosa, where a is the elevationalangle.

The operation of the instrument described hereinabove is believed to beclear from the foregoing description. It is noted that the conditionsfor various values of the elevation of tube 12 are schematicallyindicated in FIG. 1. It is clear from the foregoing if A and F representthe values of modulation signal wavelength and frequency, respectively,for zero elevation, when the value of the elevation is a thecorresponding values of modulation signal wavelength and frequency are)t/cosa and Fcosa, respectively. This formulation implies that thehorizontal projection of the modulation signal wavelength is always thesame; that is, this wavelength always has the value A. Referring to FIG.2, a presently preferred embodiment of the modulating signal source 28is shown in more detail. In general, FIG. 2 includes circuits forfacilitating the calibration of the elevational-responsive means 40through the provision of first and second control knobs 42 and 44 usedin calibrating the output signal thereof for two values of theelevation, (11 and a2. Like elements are identified by the same numeralsin FIG. 2 as in FIG. 1.

Considering FIG. 2, modulation signal source 28 includes as an essentialelement thereof a frequency-controlled oscillator 46 which may be of thetype disclosed in Swedish Pat. No. 220,951. In general, the accuracy offrequency controlled oscillator 46 is controlled by comparing the outputfrequency thereof, denoted f, with the frequency F of a masteroscillator 48 through the utilization of first and second counters 50and 52 as described hereinbelow. Master oscillator 48 is a highprecisioncrystal oscillator, the output of which is supplied to the first counter50. The capacity of counter 50 is 2n so that the output thereofcomprises an oscillation of frequency F/2n,,, which output is connectedto a frequency detector 54. The frequency f derived fromfrequency-controlled oscillator 46 is supplied to a switching circuit 56adapted to produce an output signal of frequencyforf/Z, depending uponthe position of switching circuit 56 as determined by an actuator 58.The output from switching circuit 56 is connected to second counter 52,counter 52 having a capacity n Counter 52 is connected to a storagedevice 60 in which a number n is stored, the number n having any valuefrom 0 up to n The value n is derived from the elevation-responsivedevice 40 in an analogue-to-digital converter 62, which may be of anyconventional form, in accordance with the formula Actuator 58 iscontrolled responsive to an output pulse from counter 52 and to anoutput pulse from storage device 60, the latter pulse being producedwhen the count of counter 52 has reached the value It stored in storagedevice 60.

As mentioned hereinabove, first and second control knobs 42 and 44 areassociated with elevation-responsive device 40 for adjusting the outputsignal of device 40 for two predetermined values a, and a respectively,of the angle of elevation. In the example under consideration, a, 0 anda arccos (31/32).

Counter 52 is adapted to start counting at the frequency f/2 until thecount reaches the value n. At that moment, storage device 60 produces anoutput pulse which is applied to actuator 58 and causes actuation ofswitching circuit 56 to the second position thereof in which thefrequency f is supplied to counter 52. The count then continues at thisrate until the value n is reached. At this time, an output pulse isprovided by counter 52 and is applied to frequency detector 54 andactuator 58, the latter being reset by this pulse. The result of theoperation described is that the period T of the output signal producedby counter 52 is:

T =(n -n)T+(n) 2T (2) where T is the period of the output of frequencycontrol oscillator 46. Modulating signal source 28 further includes afirst mixer 64 having a first input for receiving the output of masteroscillator 48 and a second input for receiving the output offrequency-controlled oscillator 46. A second mixer 66 includes a firstinput connected to the output of mixer 64 and a second input connectedto a stage of counter 50 in which the frequency F has been divided downto the value F/32. The outputs from mixers 64 and 66 are connected tofirst and second terminals 68 and 70 which are selectively connectableto a frequency measuring device 72 by means ofa switch 74.

First and second levels 76 and 78 are mounted integrally on tube 12 andare adapted to indicate the predetermined elevational angles a, and arespectively, as is indicated in FIG. 2.

Considering the operation of the system described hereinabove, it isreadily seen from equation (2) that the output frequency produced bycounter 52 will be f/(n n). The frequency detector 54 compares thisfrequency with the frequency F/2n produced by counter 50 and derives anoutput signal representing the difference between the two signals. Thisdifferent signal is used in adjusting the output of frequency-controlledoscillator 46 until equality is obtained between the two frequencies.Under these circumstances, the following formula holds:

f F n+nu (3) As stated hereinabove, the desired value offis f= Fcosu 4and thus it is clear from equations (3) and (4) set forth above that thevalue n supplied to storage device 60 should be determined in accordancewith equation l set forth hereinabove.

It is noted that both elevational-responsive device 40 andanalogue-to-digital converter 62 may be of conventional construction,ADC 62 producing an output n in accordance with equation (1). One formof elevational-responsive device which is suitable for use is shown inFIG. 3 and described in more detail hereinbelow.

Considering FIGS. 1 and 2 together, with analogue-todigital converter 62supplying an output n to storage device 60 as described hereinabove, thefrequency of the modulation signals applied to modulation light source20 varies in accordance with equation (4), meaning that the wavelengthof the modulation signal is inversely proportional to cosa and that themeasurement of distance will be provided in terms of the horizontalprojection of the wavelength of the modulation signal, that is, thedistance measurement provided will be the horizontal distance betweenthe instrument and the target object irrespective of the elevation ofthe instrument.

In calibrating elevation-responsive device 40 the tube 12 is first setat the angle a 0 with the aid of level 76. At this time, switch 72 isconnected to terminal 70 and thus connects mixer 64 to frequencymeasuring device 74. Control knob 42 is then adjusted until frequencymeasuring device 74 reads zero, indicating that the output frequency fF. The tube 12 is then set at the angle :1 with the aid of level 78 andswitch 72 is connected to terminal 68 so that mixer 66 is connected tofrequency measuring device 74. Control knob 44 is then adjusted untilfrequency measuring device 74 again reads zero, indicating that the twofrequencies supplied to mixer 66 are equal. As stated hereinabove, oneof these frequencies is F/32 and the other is the beat frequency frommixer 64 which latter frequency now also should have the value F/32 inthat because cosa 31/32 the frequency F should have the value 3 lF/32.

Referring to FIG. 3, there is shown an embodiment of anelevation-responsive device, generally denoted 80, in the form of aconventional accelerometer modified in accordance with the presentinvention. Elevation-responsive device 80 includes a spring 82 which isadjustable by means of a knob 84 and which serves to compensate for theforce of gravity exerted on a pendulum 86 when the pendulum 86 assumes ahorizontal position. This type of accelerometer is otherwise known perse so that only a description of the adaptation of the accelerometer forthe purposes of the present invention will be set forth. The pendulum 86is joumalled on a shaft 88 in a housing 90 and, in addition to the forceof gravity, is subject to the counteracting force provided by spring 82as set forth hereinabove and to a balancing force exerted by a magneticcoil 92. The current I through the magnetic coil 92 is supplied from acontrollable current source 94 which, in turn, is controlled by acontrol unit 96 responsive to the unsymmetrical position of pendulum 86relative to a balanced magnetic circuit 98. In a conventional manner, acontrol signal is supplied which increases or decreases the currentuntil the balance of pendulum 86 is restored and the position thereofmaintained symmetrical relative to balanced magnetic circuit 98. Thus ifthe inclination of the accelerometer 80 is a as shown, the weight of thependulum will counteract the force A exerted by the spring 82, thecounteracting force supplied by spring 82 having a value Acosa and hencethe remaining force to be exerted by magnetic coil 92 being proportionalto A Acosa. It will be understood that under these circumstances thecurrent to be supplied to the magnetic coil 92 to restore thesymmetrical position of pendulum 86 is also proportional to 1 cosa, thatis, the current I k(1cosa), In order to permit the adjustment of thevalue of the scale factor k in the formula set forth above, anadjustable potentiometer 100 is provided as indicated in FIG. 3 forcontrolling the output of current source 94.

It is noted that in some instances it may be desirable to derive asignal from the elevation-responsive means described hereinabove whichis dependent upon the sine rather than the cosine of the elevation. Itis noted that the accelerometer of FIG. 3 can easily be adapted for thispurpose by mounting the accelerometer at right angles to the positionshown in FIG. 3 so that the accelerometer is normally vertical. Thebalancing spring 82 is then no longer required and the compensatingforce necessary to be produced by the current I will, under thesecircumstances, be proportional to sine 01. However, it should be pointedout that it is not usually practical to perform a distance measurementutilizing a frequency which is equal to a value F sina in that thisfrequency will usually be unpractically low. Thus, it is more practicalto use a frequency such as F( lsina1r'/s" Although the invention hasbeen described in detail with respect to an exemplary embodimentthereof, it will be understood by those of ordinary skill in the artthat variations and modifications may be effected within the scope andspirit of the invention.

I claim:

1. An instrument for determining the projected distance to a targetobject from a point at an altitude different from that of the targetobject, comprising an optical unit for transmitting a beam of light andreceiving a beam of light along the optical axis thereof, means forvarying the elevation of said optical unit, a light transmitter forsupplying a beam of light to be transmitted by said optical unit, alight receiver for receiving the light received by said optical unit, amodulation signal source connected to said transmitter for producing amodulation signal for modulating the transmitted beam of light andhaving a control input for varying the wavelength of said modulationsignal, means for measuring the modulation phase difference between thetransmitted and received light, means responsive to the elevation ofsaid optical unit for generating a control signal in accordance with theelevation of said unit, and means for applying said control signal tothe control input of said modulation signal source.

2. An instrument as claimed in claim 1, wherein said elevationresponsive means comprises means for adjusting the value of the controlsignal for first and second predetermined values of the elevation, saidinstrument further comprising a pair of levels mounted thereon, each ofsaid levels assuming a horizontal position at a corresponding one ofsaid predetermined values of elevation.

3. An instrument as claimed in claim 2, wherein said modulation signalsource comprises a master oscillator, a frequency-controlled oscillatorand means for deriving reference frequencies from the master oscillatorcorresponding to said predetermined values of elevation and forcomparing said derived frequencies with the frequency of saidfrequency-controlled oscillator.

4. An instrument as claimed in claim 3, wherein said frequency comparingmeans comprises a first mixer having a first input for receiving thereference frequency and a second input for receiving a frequency derivedfrom the frequencycontrolled oscillator, and a frequency measuringdevice selectively connectable to the output of said mixer.

5. An instrument as claimed in claim 4 further comprising a second mixerhaving a first input connected to the output of said first mixer and anoutput selectively connectable to said frequency measuring device, and acounter having an input connected to said master oscillator and anoutput connected to a second input of said second mixer.

1. An instrument for determining the projected distance to a targetobject from a point at an altitude different from that of the targetobject, comprising an optical unit for transmitting a beam of light andreceiving a beam of light along the optical axis thereof, means forvarying the elevation of said optical unit, a light transmitter forsupplying a beam of light to be transmitted by said optical unit, alight receiver for receiving the light received by said optical unit, amodulation signal source connected to said transmitter for producing amodulation signal for modulating the transmitted beaM of light andhaving a control input for varying the wavelength of said modulationsignal, means for measuring the modulation phase difference between thetransmitted and received light, means responsive to the elevation ofsaid optical unit for generating a control signal in accordance with theelevation of said unit, and means for applying said control signal tothe control input of said modulation signal source.
 2. An instrument asclaimed in claim 1, wherein said elevation responsive means comprisesmeans for adjusting the value of the control signal for first and secondpredetermined values of the elevation, said instrument furthercomprising a pair of levels mounted thereon, each of said levelsassuming a horizontal position at a corresponding one of saidpredetermined values of elevation.
 3. An instrument as claimed in claim2, wherein said modulation signal source comprises a master oscillator,a frequency-controlled oscillator and means for deriving referencefrequencies from the master oscillator corresponding to saidpredetermined values of elevation and for comparing said derivedfrequencies with the frequency of said frequency-controlled oscillator.4. An instrument as claimed in claim 3, wherein said frequency comparingmeans comprises a first mixer having a first input for receiving thereference frequency and a second input for receiving a frequency derivedfrom the frequency-controlled oscillator, and a frequency measuringdevice selectively connectable to the output of said mixer.
 5. Aninstrument as claimed in claim 4 further comprising a second mixerhaving a first input connected to the output of said first mixer and anoutput selectively connectable to said frequency measuring device, and acounter having an input connected to said master oscillator and anoutput connected to a second input of said second mixer.